2019-Jan-25: There are two new volumes of KILLER SUDOKU out today. Enjoy!

Super-Tough Killer Sudoku, Volume 8

Each booklet contains a collection of eight different puzzles, 1-per-page, with a page of answers in the back. The booklets are ordered by ascending difficulty -- the puzzles in book 100 are much harder than the puzzles in book 1. All these puzzles have a single unique solution.